A process for the reheating and predrying of a pure gas obtained by scrubbing a flue gas from a boiler, utilizing a regenerative heat exchanger, and the regenerative heat exchanger utilized in this process are described in the journal "Energie", volume 32, number 12, December 1980, pages 463-465.
In this article, a regenerative heat exchanger takes up heat from a portion of the total quantity of flue gas branched therefrom ahead of the scrubber or washer and transfers heat to a portion of the scrubbed, washed or "cleaned" gas downstream of the washer. The resulting cooled portion of the unwashed or crude flue gas is recombined with the balance of the crude flue gas before it enters the washer and the heated portion of the cleaned gas is recombined with the balance of the cleaned gas also downstream of the washer.
Operations with such systems and the conventional regenerative heat exchanger utilized therein has shown that, in spite of the provision a droplet separator downstream of the washer, the pure gas or cleaned gas from the latter contains a high proportion of water which tends to result in contamination, soiling and corrosion in the heat storage masses of the regenerative heat exchanger and especially in deposits upon the heat exchange surfaces of the latter as the water which deposited therein evaporated.
German patent document (open application) DE-OS No. 2900275 describes a process and a device for the reheating of the clean gas following a scrubbing operation and utilizing the so-called recirculation principle. Here the flue gas from a combustion installation is passed through a dust separator and the entire quantity or flow of this flue gas before entering the scrubber is passed through the regenerative heat exchanger and cooled. Simultaneously, from the total quantity of clean gas leaving the scrubber, a portion of the clean gas is branched and, for reheating, is conducted through the regenerative heat exchanger before it is mixed with the balance of the clean gas to raise the temperature of the resulting mixture.
This latter process has been found to be effective when the flue gas leaving the combustion installation has a temperature between 250.degree. C. and 300.degree. C. which may be the case in combustion systems other than steam boilers in power plant applications. In such applications, the temperature of the flue gas downstream of the air preheater is only about 130.degree. C. and at such temperatures this prior art method cannot operate.